Rivers and Streams, Characteristics - Hydro-Environmental Analysis: Freshwater Environments - page 18

What is the difference between a river and a reservoir, or a wetland? What are the differences
between “natural” and “regulated” rivers, and how are they regulated?
It is clear that there is no precise or exact deinition of a river or stream. Whether a waterbody is a
river, stream, brook, or beck may be solely due to local custom or the whim of the cartographer who
put in on a map. However, the characteristics of rivers and streams do impact how they are managed
and regulated and are often used to classify such waterbodies. Some of their general characteristics
are described in the following sections.
2.2 CHARACTERISTICS OF RIVERS AND STREAMS
Rivers are lotic systems (lotus, from lavo , to wash), and are generally dominated by lows, which
are usually unidirectional in response to gravity, as opposed to lakes and reservoirs, which are
lentic systems ( lenis , to make calm). The characteristics of rivers and streams are strongly related
to the watershed (climate, geology, vegetative cover, etc.) and human inluences. The differences
in how rivers are organized and function have led to the development of a variety of classiication
schemes, of which some of the more common ones are discussed in this section. While the sepa-
ration is somewhat artiicial, the variations in riverine systems and their classiications are often
based on changes occurring with respect to distance, longitudinal, lateral, and vertical, and with
time (Figure 2.4). The changes are not conined to the variations within the river channel, but are on
a much broader scale, since riverine systems strongly impact the surrounding landscape. Another
major factor impacting the characteristics of rivers and their landscape is human activity. Relatively
few “natural” landscapes or unregulated or “natural” riverine systems remain.
2.2.1 S treaM c orrIdor c oncept : a L onGItudInaL V Iew
Consider a river as a “large stream,” which originates at some elevation and ultimately lows down-
stream into some other waterbody, such as an estuary or an ocean. The river may also receive,
FIGURE 2.4 The four dimensions of a lotic system. (From O'Keefe, T.C., Elliott, S.R., and Naiman, R.J.,
Introduction to watershed ecology, U.S. Environmental Protection Agency, Watershed Academy Web, 2007,
Available at http://cfpub.epa.gov/watertrain/pdf/modules/watershedecology.pdf; Based on Ward, J.V., Journal
of the North American Benthological Society , 8, 2-8, 1989. With permission.)